Adjust the oven rack to the middle position, pre-heat the oven to 350ºF (180ºC) and line a 9-inch (23cm) square baking tin with parchment/baking paper.
In a large bowl, whisk together the light brown sugar, oil, eggs and vanilla until well combined.
Sift in the gluten free flour blend, baking powder, baking soda, xanthan gum, salt, cinnamon, ginger and nutmeg.
Whisk everything together into a smooth batter with no flour clumps.
Add the coarsely grated carrots and roughly chopped walnuts, and fold them into the batter until they're evenly distributed throughout.
Transfer the batter into the lined baking tin and smooth out the top.
Bake at 350ºF (180ºC) for about 35 minutes or until well risen, golden-brown on top and an inserted toothpick/cake tester comes out clean.
Allow the cake to cool in the baking tin for about 10-15 minutes, then transfer it out of the tin onto a wire rack to cool completely.
In a large bowl, whisk the cream cheese until it's smooth and looser in texture.
Add the heavy/double cream, powdered/icing sugar and vanilla, and whisk until soft peaks form.
Spread the cream cheese frosting on top of the cooled carrot cake all the way to the edges.
Sprinkle on some extra chopped walnuts as decoration, slice and serve.
